This invention relates to improvements in or relating to self-drilling screws provided with either a single screw thread or a plurality of screw threads equal to each other in angle and height.
In the prior art, it is known to form at least one protuberance in the portion of the screw thread located in the tapering portion at the forward end of a self-drilling screw so that a swaging action may be performed. Known self-drilling screws have had disadvantages in that when no holes are formed beforehand in members which are to be fastened together by a self-drilling screw, difficulties are encountered in using a self-drilling screw for fastening together steel sheets of large thickness due to the limits placed on the capacity of the self-drilling screw by strength and other properties thereof which arise from the shape and dimensions of the forward end portion of the screw.